System, apparatus, and method for ice detection

ABSTRACT

A system, apparatus, and method for determining when an amount of ice formed on an evaporator or evaporator grid has reached a predetermined size are illustrated. An acoustic transmitter an acoustic transmitter positioned proximate to the evaporator channels acoustic signals emanating from the evaporator or evaporator grid to an acoustic sensor, which generates an electronic signal indicative of the acoustic signal. A receiver module coupled to the acoustic sensor is configured to receive the electronic signal and determine that ice formed on the evaporator has reached a predetermined size based on the electronic signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/441157, filed on Feb. 9, 2011, and incorporated herein by reference.

FIELD

The present disclosure relates to a system, apparatus, and method fordetecting an object or the lack of the presence of an object, includingthe detection of ice in an ice-forming apparatus or refrigeration caseor system.

BACKGROUND

This section provides background information related to the presentdisclosure and is not necessarily prior art.

In some ice-forming apparatuses, ice is formed from an evaporator grid.The ice grows on the evaporator grid until it reaches a desirable sizeor thickness. Once the ice has reached the desired size or thickness,the ice is harvested from the evaporator grid, thereby separating icecubes from the evaporator grid. The ice-forming apparatus determineswhen to harvest the ice, i.e., the harvest initiation point.

One technique determines water conductivity. For example, an electrodeor probe may be placed a precise distance away from the evaporator. Asthe ice forms, the water flowing over the evaporator eventually comes incontact with the probe. A conductive path via the water is formedbetween the electrode and the chassis of the machine (ground), therebyindicating that the ice has reached a predetermined size. These types ofsensors, however, have certain drawbacks. For instance, as scale formson the probe, a parallel conductive path can be formed to ground.Furthermore, extremely pure water is not conductive, thereby reducingthe effectiveness of the sensor.

Another technique may utilize capacitive sensors. For example, anelectrode may be placed a precise distance away from the evaporator. Asthe ice forms, the water flowing over the evaporator eventually comes incontact with the probe. When the water comes in contact with theelectrode, the capacitance changes and this change can be used todetermine the harvest initiation point. Capacitive sensors used in thissetting also suffer from certain drawbacks. For instance, scaling caninterfere with the capacitance reading when dirty water is used in theice-forming apparatus.

A third technique is a batch system technique. For example, in a batchsystem the water level in a sump tank may be measured. The sump isfilled to a predetermined point and then the pump is started and the icestarts to form. As ice forms, the level in the sump decreases. When thewater level decreases to a sufficient level the harvest is initiated. Adraw back with this technique is that the ice thickness may vary due tofactors such as environmental conditions (temperature, humidity), levelof total dissolved solids in the water (only the water freezes, not theminerals), and water loss in the sump (e.g., a leaking water dumpvalve). Thus, the batch system technique may not result in uniformlysized ice cubes from batch to batch.

SUMMARY

In an aspect of the disclosure, a system for determining when an amountof ice formed on an evaporator has reached a predetermined size isillustrated. The system includes an acoustic transmitter positionedproximate to the evaporator and an acoustic sensor coupled to theacoustic transmitter. The acoustic transmitter channels acoustic signalsemanating from the evaporator to the acoustic sensor and the acousticsensor generates an electronic signal indicative of the acoustic signal.The system further includes a receiver module coupled to the acousticsensor and configured to receive the electronic signal, and determinethat ice formed on the evaporator has reached a predetermined size basedon the electronic signal.

In another aspect of the disclosure, an ice-forming apparatus isdisclosed. The apparatus includes an evaporator grid, an acoustictransmitter positioned proximate to the evaporator grid, and an acousticsensor coupled to the acoustic transmitter. The acoustic transmitterchannels acoustic signals emanating from the evaporator grid to theacoustic sensor and the acoustic sensor generates an electronic signalindicative of the acoustic signal. The apparatus further includes areceiver module coupled to the acoustic sensor and configured to receivethe electronic signal, and determine that ice formed on the evaporatorgrid has reached a predetermined size based on the electronic signal.

In another aspect of the disclosure, a method for determining whetherformed ice has reached a predetermined size is disclosed. The methodincludes receiving an electronic signal indicative of an acousticsignal, transforming the electronic signal from a time domain to afrequency domain, sampling one or more amplitudes of the transformedsignal at one or more predetermined frequencies, and initiating one of aharvest operation and a defrost cycle based on the one or more sampledamplitudes.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples areintended for purposes of illustration only and are not intended to limitthe scope of the disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a drawing illustrating exemplary machinery of an ice-formingapparatus having an acoustical sensor system according to variousembodiments of the disclosure;

FIGS. 2A and 2B are drawings illustrating an exemplary acoustictransmitter in an assembled view and in an exploded view, respectively,according to various embodiments of the disclosure;

FIG. 3 is a drawing illustrating an exemplary acoustic transmitter in anassembled view according to various embodiments of the disclosure;

FIG. 4 is a drawing illustrating an exemplary acoustic sensor systemaccording to various embodiments of the disclosure; and

FIG. 5 is a flow chart illustrating an exemplary method for determiningwhen formed ice has reached a predetermined size according to variousembodiments of the disclosure.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

The current disclosure describes an apparatus that enables detection ofobjects or material (collectively, an “object” or “objects”). Examplesof objects, articles, or material which may be detected by the apparatusand method include, but are not limited to, solid objects or materialsuch as ice. Examples of object- or material-processing systems include,but are not limited to ice-forming machines and ice-collection bins ofice-making systems. Other example applications may include refrigerationcases, bins, freezers, display cases, and other devices or refrigerationstorage containers, where the detection system may be used to detect anaccumulation of ice and initiate a defrost procedure.

FIG. 1 illustrates an exemplary ice-forming apparatus 100. An exemplaryice-forming apparatus 100 can include an evaporator 110, an acoustictransmitter 120 that transmits acoustic signals, a receiver module 130,and a flexible acoustical transmission tube 140 that channels theacoustic signals from the acoustic transmitter 120 to the receivermodule 130. The receiver module 130 processes electronic signalscorresponding to the acoustic signals and controls the evaporator 110based thereon.

In an exemplary embodiment, the evaporator 110 can include an evaporatorgrid 160, an evaporator coil (not shown) and a cold plate (not shown).The evaporator grid 160 is used to form ice cubes. Water is pumped froma water reservoir (not shown) onto the cold plate, which is maintainedat a temperature below a freezing temperature, e.g., less thanthirty-two (32) degrees Fahrenheit or zero (0) degrees Celsius. Theevaporator grid 160 can be formed in the shape of the ice that is to beharvested from the evaporator grid 160, e.g., a cubic or rectangularprism. When the ice has a desired depth or thickness, the ice can beharvested using known techniques. For instance, the evaporator grid 160may be heated such that the formed ice cubes break and separate from theevaporator grid 160.

The ice-forming apparatus 100 shown in FIG. 1 can be a verticalice-forming apparatus 100, wherein water flows from the top of thevertical ice-forming apparatus 100 over a vertical evaporator grid 160.It is appreciated that the techniques disclosed herein may be applied toany other type of ice-forming apparatuses 100 or to any other types ofapparatus that incorporates an evaporator 110, e.g., a refrigerationapparatus and an air conditioner.

The receiver module 130 controls whether the evaporator 110 is formingice or harvesting ice. When the formed ice has reached a sufficient sizeor thickness, the receiver module 130 initiates a harvesting operation,e.g., instructs the evaporator 110 to heat the evaporator grid 160 toharvest the ice. The receiver module 130 can be configured to receiveelectronic signals indicative of the acoustic signals channeled from theacoustic transmitter 120. As described in further detail below, anacoustic sensor can receive an acoustic signal and generate theelectronic signal corresponding to the acoustic signal. The acousticsignal (and the electronic signal) can provide an indication of the sizeof the formed ice, e.g. the depth or thickness of the formed ice.

In some embodiments, the receiver module 130 processes the electronicsignal received from the acoustic sensor to sample the amplitude of theelectronic signal at certain predetermined frequencies. When theamplitude of the electronic signal at the predetermined frequencies (ora subset of the predetermined frequencies) exceeds correspondingpredetermined thresholds, the receiver module 130 determines that theformed ice has reached sufficient size or thickness and initiates aharvesting operation. In other words, when the amplitude of the acousticsignals at the predetermined frequencies (or a subset of thepredetermined frequencies) exceeds the corresponding predeterminedthresholds, the receiver module 130 determines that the harvestinitiation point has been reached and initiates the harvest.

The acoustic transmitter 120 can be positioned in proximity to theevaporator grid 160. The focal points of the diaphragm of the acoustictransmitter, discussed in greater detail below, can be positioned toface the evaporator grid 160. The acoustic transmitter 120 may pick upand transmit the background noise or frequencies of the ice-formingapparatus 100, or other device or machinery within which it isinstalled. As the ice grows, the ice can form and grow towards theacoustic transmitter 120. Once the ice physically touches the acoustictransmitter 120, there is a significant increase in the amplitude of thenoise signal generated by the ice-forming apparatus 100, e.g., noiseresulting from mechanical vibration from the ice-forming apparatus 100.When there is no physical contact between the acoustic transmitter 120and the ice formed on the evaporator grid 160 100, the noise emanatingfrom the ice-forming apparatus 100 is transferred via the air and theamplitude of the noise signal is reduced. The acoustic signals that arepicked up by the acoustic transmitter 120 can be transferred to anacoustic sensor (not shown) via the flexible acoustical transmissiontube 140.

In some embodiments, the acoustic transmitter 140 can be used to measurethe “bridge thickness” of the ice. The diaphragm of the acoustictransmitter 120 can be placed relatively close to the evaporator grid160, e.g., one-eight (⅛) of an inch, so as to measure the bridgethickness. The bridge thickness is indicative of the overall depth orthickness of the formed ice.

In some embodiments, a wall 150 can separate the receiver module 130 andother electronics from the evaporator 110. As will be discussed infurther detail, an acoustic sensor, e.g., a microphone, can be locatedat the evaporator grid 160 side of the wall 150, or at the receivermodule 130, such that the acoustic signal is transferred to the acousticsensor via the flexible acoustical transmission tube 140.

In some embodiments, the acoustic transmitter 120 may be placedproximate to an evaporator 110 of a refrigeration case, a refrigerationbin, a freezer, a refrigeration display case, and other types ofrefrigerated storage containers. In these embodiments, the acoustictransmitter 120 can be positioned near an area of the evaporator 110where ice typically accumulates, e.g., the fins of the evaporator 110,so that the receiver module 130 can determine whether the accumulatedice has exceeded a predetermined level. When the receiver module 130determines that the accumulated ice has exceeded the predeterminedlevel, the receiver module 130 can initiate a defrost operation, such ascommencing a defrost cycle.

FIGS. 2A and 2B illustrate an exemplary acoustic transmitter 120 in anassembled view and an exploded view, respectively. In some embodiments,the acoustic transmitter 120 can include an acoustic transmitter frame210, an acoustic diaphragm 220, a flexible acoustical transmission tube140, an interface 240 that couples the flexible acoustical transmissiontube 140 to the acoustic diaphragm 220, and a height-adjustment screw250.

In some embodiments, the acoustic transmitter 120 includes the acoustictransmitter frame 210 and the acoustic diaphragm 220. The acoustictransmitter frame 210 can include a substantially circular portion thatforms an acoustical chamber 260. The substantially circular portionreceives the acoustic diaphragm 220. It should be appreciated that theacoustic chamber 260 can be formed in any suitable shape.

The acoustic diaphragm 220 can be a thin membrane that vibrates when thepressure caused by sound waves is imparted on the acoustic diaphragm220. The vibration of the acoustic diaphragm 220 causes an acousticsignal, e.g., a sound wave, to reverberate throughout the acousticalchamber 260. The acoustic diaphragm 220 can include a plurality of focalpoints 230-A and 230-B. The focal points 230-A and 230-B can bepositioned facing and substantially parallel to the evaporator grid 160(FIG. 1).

In some embodiments, the acoustic transmitter frame 210 can include theinterface 240, which is configured to receive the flexible acousticaltransmission tube 140. The flexible acoustical transmission tube 140 canbe forcibly inserted onto or into the interface 240, such that acousticsignals amplified by the acoustic diaphragm 220 are channeled to theacoustic sensor through the flexible acoustical transmission tube 140.As will be discussed in further detail below, the acoustical signals canbe received by the acoustic sensor which outputs electrical signalsindicative of the acoustic signal to the receiver module 130.

In some embodiments, the acoustic transmitter 120 can include aheight-adjustment screw 250. The height-adjustment screw 250 canprotrude perpendicularly from the frame 210. The height-adjustment screw250 can be utilized to adjust a distance between the acoustictransmitter 120 and the evaporator grid 160. As should be appreciatedfrom FIG. 2B, the height-adjustment screw 250 can be inserted into anopening in the frame 210. The height-adjustment screw 250 can be screwedin to increase the distance between the acoustic transmitter 120 and theevaporator grid 160. It should be appreciated that other means forcontrolling the distance between the acoustic transmitter 120 and theevaporator grid 160 are contemplated and are within the scope of thisdisclosure.

It should be appreciated that the acoustic transmitter 120 of FIGS. 2Aand 2B are provided for example only and not intended to be limiting.Variations of the acoustic transmitter 120 are contemplated and arewithin the scope of the disclosure.

FIG. 3 illustrates an alternative embodiment of an acoustic transmitter300. For purposes of explanation, components appearing in the acoustictransmitter 120 of FIGS. 2A and 2B and in the acoustic transmitter 300of FIG. 3 have been provided the same reference numbers.

In some embodiments, the acoustic transmitter 300 may include anacoustic sensor 270 coupled to the interface 240. In these embodiments,the acoustic sensor 270 can be mounted to the interface 240 such thatthe acoustic signals emanating from the acoustic diaphragm 220 arechanneled directly to the acoustic sensor 270. The acoustic sensor 270receives the acoustic signal and outputs an electronic signal indicativeof the received acoustic signal to the receiver module 130. It should beappreciated that the acoustic sensor 270 can be any suitable microphone.It should be further appreciated that other types of acoustic sensors270 can be used, such as sound transducers or piezoelectric transducers.

FIG. 4 illustrates an example acoustic transmitter system 400. In someembodiments, the acoustic transmitter system 400 can include theacoustic transmitter 120, the flexible acoustical transmission tube 140,the acoustic sensor 270, the receiver module 130, and a housing 410. Ascan be appreciated, the exemplary acoustic transmitter 120 describedwith respect to FIGS. 2A and 2B is connected to the receiver module 130by the acoustical transmission tube.

In the illustrated example, the receiver module 130 includes an acousticsensor 270, a circuit board assembly 420, and a receiver clip 430, allof which can be housed in the housing 410. The receiver clip 430 is anysuitable fastener that fastens the flexible acoustical transmission tube140 to the acoustic sensor 270. It is appreciated that other acousticsensors can be used, such as sound transducers or piezoelectrictransducers. The acoustic signals are channeled from the acoustictransmitter 120 to the acoustic sensor 270, which converts the receivedacoustic signal into an electronic signal that is able to be processedby the receiver module 130, e.g., a digital signal.

As should be appreciated from the illustrated example, the acoustictransmitter 120 can be placed proximate to an evaporator grid 160 (FIG.1). It should be appreciated that while the acoustic transmitter 120 isexplained as being proximate to an evaporator grid 160, the techniquesdisclosed herein are applicable to any type of evaporator 110. In someembodiments, the acoustic transmitter 120 can be positioned such thatthe focal points 230-A and 230-B (FIGS. 2A and 2B) of the acousticdiaphragm 220 (FIGS. 2A and 2B) face the evaporator grid 160. Theacoustic sensor 270 may be coupled to the acoustic transmitter 120. Inthe illustrated example, the flexible acoustical transmission tube 140is interposed between the acoustic transmitter 120 and the acousticsensor 270. The acoustic transmitter 120 channels acoustic signalsemanating from the evaporator grid 160 to the acoustic sensor 270. Theacoustic sensor 270 can generate an electronic signal indicative of theacoustic signal, which is provided to the receiver module 130.

The receiver module 130 can be electrically coupled to the acousticsensor 270 such that the receiver module 130 is configured to receivethe electronic signal. The receiver module 130 can be further configuredto determine that ice formed on the evaporator grid 160 has reached apredetermined size based on the electronic signal. When the ice formedon the evaporator grid 160 extends from the evaporator grid 160 andphysically connects to the acoustic diaphragm 220, amplitude of theacoustic signal transmitted by the acoustic transmitter 120 mayincrease. Thus, the receiver module 130 can continuously monitor theamplitudes of the electronic signal to determine when to initiate an iceharvesting operation or a defrost operation.

In some embodiments, the receiver module 130 can be configured totransform the electronic signal to a frequency domain and sample one ormore amplitudes of the transformed electronic signal at one or morepredetermined frequencies. In some of these embodiments, the receivermodule 130 can compare each of the one or more sampled amplitudes to acorresponding predetermined amplitude threshold, such that when one ormore of the sampled amplitudes exceeds its corresponding predeterminedamplitude threshold, the receiver module 130 determines that the ice hasreached the predetermined size. In other embodiments, the receivermodule 130 can determine that the ice has reached the predetermined sizewhen all of the sampled amplitudes exceed their correspondingpredetermined amplitude thresholds.

It is noted that for each ice-forming apparatus 100, refrigeration case,air-conditioner, or the like, the frequencies at which the amplitudesmay be sampled are determined during a testing phase. Depending onfactors such as the size of the cavity of the ice-forming apparatus 100,the machinery of the ice-forming apparatus 100, or other pertinentfactors, such as the compressor operating frequency of the ice-formingapparatus 100, one or more frequencies are determined to be appropriatefor sampling. For example, in some embodiments, it may be determinedthat the amplitudes can be sampled at 60 Hz, 120 Hz, 180 Hz, and 240 Hz.

During the testing phase, the amplitude thresholds for a particularice-cube size that correspond to the predetermined frequencies are alsodetermined. For instance, for a first frequency, a first amplitudethreshold can be determined, for a second frequency, a second amplitudethreshold can be determined, etc., to an nth frequency, for which an nthamplitude threshold can be determined. Once the frequencies andthresholds have been determined, the receiver module 130 can beconfigured to sample the transformed electronic signal at thefrequencies and to determine whether the ice is ready for harvestingbased on the amplitudes of the electronic signal at the frequencies.

FIG. 5 illustrates an exemplary method 500 that may be executed by thereceiver module 130. The method 500 may start executing when theice-forming apparatus 100 is operating in a freezing mode or when arefrigeration case or system is operating in a cooling cycle. At 510,the receiver module 130 can receive the electronic signal indicative ofthe acoustic signal from the acoustic sensor 270. At 512, the receivermodule 130 can transform the electronic signal to the frequency domain.In some embodiments, a Fast Fourier Transform (FFT) is performed on theelectronic signal to transform the electronic signal from the timedomain to the frequency domain. It should be appreciated that anysuitable transformation technique can be implemented by the receivermodule 130. For instance, the receiver module 130 can implement aDiscrete Fourier Transform, Laplace Transforms, or Z-Transforms totransform the electronic signal to the frequency domain.

At 514, the receiver module 130 can sample the transformed electronicsignal at one or more predetermined frequencies. At 516, the receivermodule 130 can compare each of the sampled frequencies to acorresponding frequency threshold. If the amplitudes at a predeterminednumber of frequencies exceed their respective frequency threshold, thereceiver module 130 can determine that the formed ice is of sufficientsize and/or thickness. In this scenario, the receiver module 130 caninitiate a harvest event or a defrost cycle, as shown at 518. It shouldbe appreciated that in some embodiments, the receiver module 130 mayrequire that all of the sampled amplitudes exceed their respectivefrequency threshold, or one, two, three, or more amplitudes exceed theirrespective frequency thresholds. If the receiver module 130 determinesthat the requisite number of amplitudes exceeding the respectiveamplitude threshold was not met, the receiver module 130 returns to 510.

It is appreciated that the method 500 provided above has been providedfor example only and is not intended to limit the scope of thedisclosure. Variations of the method 500 are within the scope of thedisclosure.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. For purposes of clarity, thesame reference numbers will be used in the drawings to identify similarelements. As used herein, the phrase at least one of A, B, and C shouldbe construed to mean a logical (A or B or C), using a non-exclusivelogical OR. It should be understood that one or more steps within amethod may be executed in different order (or concurrently) withoutaltering the principles of the present disclosure.

As used herein, the term module may refer to, be part of, or include anApplication Specific Integrated Circuit (ASIC); an electronic circuit; acombinational logic circuit; a field programmable gate array (FPGA); aprocessor (shared, dedicated, or group) that executes code; othersuitable hardware components that provide the described functionality;or a combination of some or all of the above, such as in asystem-on-chip. The term module may include memory (shared, dedicated,or group) that stores code executed by the processor.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes,and/or objects. The term shared, as used above, means that some or allcode from multiple modules may be executed using a single (shared)processor. In addition, some or all code from multiple modules may bestored by a single (shared) memory. The term group, as used above, meansthat some or all code from a single module may be executed using a groupof processors. In addition, some or all code from a single module may bestored using a group of memories.

The apparatuses and methods described herein may be implemented by oneor more computer programs executed by one or more processors. Thecomputer programs include processor-executable instructions that arestored on a non-transitory tangible computer readable medium. Thecomputer programs may also include stored data. Non-limiting examples ofthe non-transitory tangible computer readable medium are nonvolatilememory, magnetic storage, and optical storage.

1. A system comprising: an acoustic transmitter positioned proximate toan evaporator, an acoustic sensor coupled to the acoustic transmitter,wherein the acoustic transmitter channels acoustic signals emanatingfrom the evaporator to the acoustic sensor and the acoustic sensorgenerates an electronic signal indicative of the acoustic signal; and areceiver module coupled to the acoustic sensor and configured to receivethe electronic signal and determine that ice formed on the evaporatorhas reached a predetermined size based on the electronic signal.
 2. Thesystem of claim 1, wherein the receiver module is further configured totransform the electronic signal to a frequency domain and sample one ormore amplitudes of the transformed electronic signal at one or morepredetermined frequencies.
 3. The system of claim 2, wherein thereceiver module is further configured to compare each of the one or moresampled amplitudes to a corresponding predetermined amplitude threshold,wherein when at least one of the one or more sampled amplitudes exceedsits corresponding predetermined amplitude threshold, the receiver moduledetermines that the ice has reached the predetermined size.
 4. Thesystem of claim 2, wherein the receiver module is further configured tocompare each of the one or more sampled amplitudes to a correspondingpredetermined amplitude threshold and determine that the ice has reachedthe predetermined size when all of the one or more sampled amplitudesexceed the corresponding predetermined amplitude thresholds.
 5. Thesystem of claim 4, wherein the receiver module is further configured toinitiate one of a harvesting operation and a defrost operation when theice has reached the predetermined size.
 6. The system of claim 1,wherein the receiver module is further configured to initiate one of aharvest operation and a defrost operation when the ice has reached thepredetermined size.
 7. The system of claim 1 wherein a diaphragm of theacoustic transmitter is positioned such that a focal point of thediaphragm faces the evaporator, whereby when the ice extends from theevaporator and physically connects to the diaphragm an amplitude of theacoustic signal transmitted by the acoustic transmitter increases. 8.The system of claim 7, further comprising a flexible acousticaltransmission tube interposed between the diaphragm of the acoustictransmitter and the acoustic sensor.
 9. The system of claim 1, whereinthe evaporator includes an evaporator grid, such that the acoustictransmitter is positioned proximate to the evaporator grid.
 10. Anapparatus comprising: an acoustic transmitter that channels acousticsignals emanating from an evaporator grid to an acoustic sensor thatgenerates an electronic signal indicative of the acoustic signal; and areceiver module coupled to the acoustic sensor and configured to receivethe electronic signal and determine that ice formed on the evaporatorgrid has reached a predetermined size based on the electronic signal.11. The apparatus of claim 10, wherein the receiver module is furtherconfigured to transform the electronic signal to a frequency domain andsample one or more amplitudes of the transformed electronic signal atone or more predetermined frequencies.
 12. The apparatus of claim 11,wherein the receiver module is further configured to compare each of theone or more sampled amplitudes to a corresponding predeterminedamplitude threshold and determines that the ice has reached thepredetermined size when at least one of the one or more sampledamplitudes exceeds its corresponding predetermined amplitude threshold.13. The apparatus of claim 11, wherein the receiver module is furtherconfigured to compare each of the one or more sampled amplitudes to acorresponding predetermined amplitude threshold and determine that theice has reached the predetermined size when all of the one or moresampled amplitudes exceed the corresponding predetermined amplitudethresholds.
 14. The apparatus of claim 10, wherein the receiver moduleis further configured to initiate a harvesting operation when the icehas reached the predetermined size.
 15. The apparatus of claim 10wherein a diaphragm of the acoustic transmitter is positioned such thata focal point of the diaphragm faces the evaporator grid, whereby whenthe ice extends from the evaporator grid and physically connects to thediaphragm an amplitude of the acoustic signal transmitted by theacoustic transmitter increases.
 16. The apparatus of claim 15, furthercomprising a flexible acoustical transmission tube interposed betweenthe diaphragm of the acoustic transmitter and the acoustic sensor.
 17. Amethod comprising: receiving an electronic signal indicative of anacoustic signal; transforming the electronic signal from a time domainto a frequency domain; sampling one or more amplitudes of thetransformed signal at one or more predetermined frequencies; andinitiating one of a harvest operation and a defrost cycle based on theone or more sampled amplitudes.
 18. The method of claim 17, furthercomprising: comparing each of the one or more sampled amplitudes to acorresponding predetermined amplitude threshold; and initiating the oneof the harvest operation and the defrost cycle when at least one of theone or more sampled amplitudes exceeds its corresponding predeterminedamplitude threshold.
 19. The method of claim 17, further comprising:comparing each of the one or more sampled amplitudes to a correspondingpredetermined amplitude threshold; and initiating the one of the harvestoperation and the defrost cycle when all of the one or more sampledamplitudes exceeds the corresponding predetermined amplitude thresholds.